Patent GB-170378-A (GB)
Title: Improvements in and relating to modulation systems and the like in radio communication and the like
IPC: H03C1/14
Filed: 1920-07-17
Abstract: 170,378. Taggart, J. Scott-, and Radio Communication Co., Ltd. July 17, 1920. Thermionic modulating systems; audible reception of unmodulated continuous waves.- In wireless transmitting and receiving systems, a current-absorbing device comprises a conductor having asymmetric and preferably unilateral conductivity, such as a rectifier. to which separate current variations are applied, said variations being applied to the main electrodes of the rectifier, thus distinguishing it from a threeelectrode valve operating as a relay. The rectifier preferably has a potential across its electrodes such that normally no current due to high-frequency oscillatory potentials flows through it, the separate applied potentials, usually of audio frequency, causing variations in this normal potential and allowing correspondingly varying amounts of the high-frequency current to pass. The rectifier may be a two-electrode valve, a fixed negative potential being applied to the anode, or a three-electrode valve, the fixed negative potential being applied to the grid, the high and low frequency current variations being applied to the anode and cathode in each case. As applied to wireless telephony, Fig. 3, a rectifier V is connected in parallel with an aerial inductance S which has in series a source H of high-frequency current. A battery B has such a value that a variation of anode voltage produced by a microphone M varies high-frequency current absorbed by the rectifier V. The battery B may be adjusted so that the valve V only conducts whilst speaking, or so that it normally absorbs energy, which absorption is varied by the modulating potentials; or the potential of the anode A may be made zero, only the negative half-cycles of the modulating potentials being applied. To obtain absorption over both half-cycles of the highfrequency currents, two opposed rectifiers may be used. Figs. 4 and 5 show two such arrangements in which the rectifiers V<1>, V<2>, are connected across an oscillatory circuit CS or any other part of a signalling system. Alternatively a rectifier having two anodes and a single filament may be used. In another arrangement, an oscillatory circuit carrying the high-frequency current, and the absorbing-rectifier are connected in parallel across the grid and filament of an amplifying valve, or a circuit containing the high-frequency source and the absorbing-rectifier in parallel, may be coupled to the grid circuit of an amplifying-valve. When large currents are to be absorbed, a number of absorbing-rectifiers V. V<2>, V<3>, Fig. 8, may be connected in parallel, their negative potentials being graded so that their conductivity varies in succession. In any of the above arrangements involving a current-absorbing rectifier, means for dissipating the absorbed energy such as resistances R<1>, R<2>, R<3>, Fig. 8, shunted by condensers may be included in each anode circuit. As applied to receiving systems, continuous waves may be modulated according to this invention, so as to be audible after rectification. One Provisional Specification also states that the absorbing device may be connected across the anode or grid oscillatory circuit of a valve either oscillating itself, or acting as an amplifier of separately produced oscillations. Specification 169,250 is referred to.